Printed wiring circuit boards, sometimes referred to simply as circuit boards, have a widespread use in electrical circuit apparatus manufactured by electrical and communications industries. Typically, circuit components are mounted on a circuit board and circuit patterns fabricated on the board interconnect the components to form a composite electrical circuit. The circuit patterns are extended to a plurality of contact or conducting fingers formed adjacent one edge of the board that are used with plug-in types of connectors to interconnect a number of circuit boards and thereby form a larger composite electrical circuit.
Sometimes when an electrical circuit on a circuit board is connected through a plug-in connector to other circuit boards, the circuit fails to operate. The operational failure may result from a circuit fault or, as sometimes happens, from a poor connection or no connection at all between the circuit board conducting fingers and the contacts of a connector. This latter type of failure may arise either because some particulate matter or a film formation has appeared on the surfaces of the circuit board conducting fingers so that the conducting fingers fail to make electrical connection with the connector contacts. In many instances particulate matter or a contamination film formation inadventently appears on the conducting fingers of a circuit board while the circuit board is being manufactured or repaired. Subsequently, the newly manufactured or repaired circuit board may be shipped to another location and installed into connector apparatus to form a composite electrical circuit. Often times the electrical circuit fails to operate in that particulate or foreign matter and contamination film appearing on the installed circuit board conducting fingers result in a poor or open connection. Locating these types of circuit failures is extremely difficult.
Measurement techniques for measuring resistance of conductive elements have been disclosed in the prior art as evidenced by U.S. Pat. No. 3,974,443. These measurement techniques, sometimes referred to as a socalled four-point contact resistant measurement, are accomplished by applying a known constant current to two outer points of a conductive element and measuring the voltage appearing between two inner points of the same contact area. A problem with the apparatus used to make a four-point conductor element resistant measurement is that the prior art apparatus, as illustrated by U.S. Pat. No. 3,996,514, is bulky in size and requires that sufficient space be available in order to gain access to the measurement points. The aforementioned problem is highlighted with the prior art measuring apparatus as disclosed by U.S. Pat. No. 3,335,365 in that the apparatus is used only to measure the resistivity of a conductive element and is not suitable for use during the process of manufacturing or repairing of circuit boards to quickly detect and measure foreign material and contamination films on the plurality of conducting fingers of a circuit board.
Accordingly, a need exists in the art for apparatus arranged to detect and measure foreign material and contamination films on a circuit board conducting finger. A need also exists for apparatus arranged for use during the process of manufacturing or repairing a circuit board to rapidly detect and measure foreign material and contamination films inadventently occurring on ones of a plurality of conducting fingers of a circuit board.